This invention relates generally to molded plastic components for use in a printing machine, and more particularly concerns molded plastic components with integral apertures.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
In modern printing machines, such as those described above, efforts are used to utilize modern lightweight and low cost recyclable materials. Chief among these low cost lightweight materials are plastics. These plastic components are molded, typically in a molding machine. For example, with a screw type auger or hydraulic ram in which the molded material is compressed and liquefied to conform to a shape of a mold. Many of these plastic components represent housings and supports which support rotating elements. Therefore, many of these plastic housings and supports require the inclusion of an aperture or bore to which the shaft may be secured.
To permit the removal of a plastic part from a mold cavity, the mold cavity typically has at least two portions or halves which are separated in order to remove the molded article. While it is somewhat simple to provide a bore or opening in a direction normal to the contact surface or parting line between the mold halves, frequently for more complex housings bores and apertures must be located in directions that are often normal to each other. Therefore, it becomes necessary to provide apertures or bores that are located in a direction parallel to the parting line or surface at which the die halves mate. To provide an aperture that has a centerline parallel to the parting line, it is necessary to have the centerline of the aperture coincident with the parting line. This configuration can be obtained by placing one half of the whole workpiece in each of the die half. When this is done, the hole often requires a side pull or a third die component in a direction parallel with the axis of the hole. Alternatively, a secondary operation such as drilling may be required to provide a bore or aperture with sufficient roundness and size control. The use of side pulls and secondary operations such as drilling adds significantly to the cost of the plastic component.
The plastic components mentioned above are used throughout the printing machine. The use of lightweight and low cost materials is particularly important in those components that must be removed by the machine operator and those components which have a life less than that of the printing machine. One common application where components have a life less than that of the machine is in a CRU, a customer replaceable unit, which cannot be replaced by the customer at the end of the life or at the premature failure of one of the xerographic components.
In printing machines such as those described above, a CRU is a customer replaceable unit which can be replaced by a customer at the end of life or at the premature failure of one or more of the xerographic components. The CRU concept integrates various subsystems whose useful lives are predetermined to be generally the same length. The service replacement interval of the CRU insures maximum reliability and greatly minimizes unscheduled maintenance service calls. Utilization of such a strategy, allows customers to participate in the maintenance and service of their copiers/printers. CRUs insure maximum up time of copiers and minimize downtime and service cost due to end of life or premature failures.
It is desirable to have a CRU that enables a variety of machine subsystems to be incorporated into a single unit while maximizing the useful life of each component. It is further desirable to utilize a CRU that allows service to a machine to be performed efficiently and at a relatively low cost and in some cases to be serviced by the user himself. It is a further benefit to have the ability to reuse and recycle various CRU components in today's climate of environmental awareness.
The lightweight low cost molded plastic components mentioned above are particularly well suited for a customer replacement unit. The CRU includes a number of shafts and other rotating and pivoting components which must be secured to bores or apertures. Many of these components within a CRU require the use of components with bores which are normal with each other which require the use of side pulls or secondary operations such as drilling to provide for an accurate bore that has a centerline parallel to the parting line of the mold.
With the cycling of a molding machine and with the separation of the molded part from the mold, over time, the surface of the mold wears. This is particularly true for the mating surfaces of each of the two or more die halves or partitions that mate to form the shape of the plastic component. Further, in order to insure that the plastic component does not have a void or lacks material in a particular part within the molding machine, typically the mold is filled with excess material which may leak at the surfaces between the mold halves. The mold halves also wear at their contact surfaces so that a parting line forms between each of the mold halves. It is the presence of the parting line and the flash that occurs at the parting line that fills partially the bores and apertures that are created along the parting line. To remove the flash at the parting line, the side pulls and the drilling operations are required.
The present invention is directed to alleviate at least some of the aforementioned problems.
More recently, plastic components have been designed which have a hole or bore with an axis parallel to the parting line in which the hole or aperture is molded in halves with two or three halves resulting in a full hole. Such a plastic component is shown in FIG. 2. The plastic component 1 includes a pair of front cavities 2 which overlap with a rear cavity 3. The central portions of the cavities 2 and 3 are semi circular whereby the cavities 2 and 3 combine to form an aperture bore 4 having an axis CC in the vertical direction. The plastic component 1 is molded from a pair of molds and has a parting line on a plane formed by axis CC and line DD which is perpendicular to aperture axis CC.
Now referring to FIGS. 3 and 4, a pair of die plates 5 and 6 respectively are shown. For simplicity, the die plates 5 and 6 show only the features required to provide the cavities to the plastic component 1 of FIG. 2. As shown in FIG. 3, the first die plate 6 includes a front die plate protrusion 7. The front die plate 7 is used to form the rear cavity 3 of the plate component 1 of FIG. 2.
Referring now to FIG. 4, the second die plate 8 preferably includes two second die plate protrusions 9. The second die plate protrusions 9 form the front cavities 2 of FIG. 2. To provide the aperture bore 4, the second die protrusions 9 are spaced apart a distance equal to the thickness of the first die plate protrusion 7 so that the upper and lower surfaces of the first die protrusions 7 are in mating contact with the inner surfaces of the second die protrusions 9.
As the opposed faces of the first die plate protrusions 7 wear against the inner surfaces of second die plate protrusions 9, a gap is formed between the protrusions 7 and 9. The gap between the protrusions results in flash 5 as shown in FIG. 2 which progresses inwardly into the aperture bore 4. The presence of the flash 5 requires that secondary operations such as drilling are required to provide for an accurate bore 4.
The following disclosures may relate to various aspects of the present invention.
U.S. Pat. No. 5,580,507 PA1 Patentee: Williamson et al. PA1 issue Date: Dec. 3, 1996 PA1 U.S. Pat. No. 5,435,959 PA1 Patentee: Williamson et al. PA1 Issue Date: Jul. 25, 1995 PA1 U.S. Pat. No. 5,262,899 PA1 Patentee: lizuka PA1 Issue Date: Nov. 16, 1993 PA1 U.S. Pat. No. 5,244,606 PA1 Patentee: Maus et al. PA1 Issue Date: Sep. 14, 1993 PA1 U.S. Pat. No. 4,895,268 PA1 Patentee: Hyde PA1 Issue Date: Jan. 23, 1990
Some portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,580,507 discloses a method of making a mold from a model. The aperture has a configuration generally corresponding to the shape of the model. A mold is formed around a model and the model is removed. Material is then placed into the mold to form the part.
U.S. Pat. No. 5,435,959 discloses a method of making a mold from a model. The aperture has a configuration generally corresponding to the shape of the model. A mold is formed around a model and the model is removed. Material is then placed into the mold to form the part.
U.S. Pat. No. 5,262,899 discloses an optical apparatus having a mount molded of plastic including a mount sliding surface formed on the mount and providing a fiducial surface in the direction of the optic axis, and a depression formed in the area of a parting line during molding on the mount sliding surface.
U.S. Pat. No. 5,244,606 discloses a molded disk which is transferred out of the mold with short stroke low-mass motions of a pair of mechanical guides which can grip, then release, the O.D. edge of the molded disk, when acting in coordination with movable mold members have in undercuts for molded on retention of the inner portion of the molded disk.
U.S. Pat. No. 4,895,268 discloses a blow molding process for making products that have at least one substantially solid attachment projection unitary with and projection outwardly from an exterior wall. The process includes the step of enclosing a molten plastic parison within a cavity formed by cooperating blow molding die parts, a void in fluid communication with with such cavity and having a configuration corresponding to that desired for the attachment projection being provided at a parting line.